Transformer



c. P. B OUC HER Y TRANSFORMER March 13, 1945.

Original Filed May 1, 1940 2 Sheets-Sheet 1 X dd m a a w %4 w March 13, 1945 I c. P. BOUCHER I 2,371,576

' TRANSFORMER Original Filed May 1, 1940 2 Sheets-SheetZ Patented Mar. 13, 1945 TRANSFORMER Charles Philippe Boucher, Fostoria, Ohio, assignor to Boucher Inventions, Ltd., Washington, D. C., a corporation of Delaware Original application May 1,. 1940, Serial No. 332,813, now Patent- N 2,312,868, dated March 2, 1943. Divided and t is application February 20, 1943. Serial No. 476.587

1 Claim. (Cl. 171-119) withstand the many varying conditions of load and ,whole or partial short-circuit encountered in actual practical use.

Another object is the provision of power transformer apparatus which is exceedingly compact,

highly efficient and particularly economical in construction, installation and operation, enjoying low copper and iron losses, a highv rate of heat dissipation and good operating power factor.

Still another object is to provide a transformer having shunt core' members which can be manufactured inexpensively and which are so designed that after assembly the shunt paths of which they form parts will have the correct predetermined magnetic reluctances.

Other'objects will be invpart obvious part pointed out hereinafter.

The invention accordingly consists in the comand. in h bination of elements, features of construction 1 and arrangement of parts, the scope of the application of which is indicated in the claim at the end of the specification.

In the accompanying drawings, Figure 1 is a diagrammatic representation of a core-type transformer embodying certain features of my invention.

Figure 2 is a similar representation of a shelltype transformer also embodying certain features of my invention.-

Figure 3 i a detail view of one pair of the core shunt pieces used in the transformer of Figure 2.

showing the means for securing them in position, and

Figure 4 is aside view of the parts shown'in Figure 3.

Like reference characters denote like parts I throughout the'several views of the drawings.

, As conducive to a more thorough understanding of my inventions, it may be noted that in the operation of a luminescent sign employing one or more luminescent gas-filled tubes high potential electrical energy is required. The desired high potential electrical energy ordinarily of luminescent tubes.

is supplied by alternating current transformer apparatus connected to a standard single phase sixtycycle source at either one hundred and ten volts or two hundred and twenty volts. The high potential electrical energy has a maximum value of about fifteen thousand volts across the terminals of the tubes or about seven thousand five hundred volts to ground. This is approximately the maximum value permitted by the fire under- 'writrs.

In the operation of even a single luminous sign or display, it often is necessary to use a plurality Since the maximum voltage to ground permitted by the fire underwriters is approximately seven thousand five' hundred volts, and consequently the maximum permissible voltage across any secondary circuit is approxi-- mately fifteen thousand volts, tubes whose striking potential is in the neighborhood of fifteen thousand volts may not be connected in 'a series circuit. Also, due to their different striking potentials and negative load operating characteristics they cannot be operated in a parallel circuit. Accordingly, each tube.must have its own separate transformer secondary winding. In, order to avoid the high costs of transformer equipment and installation which would be incurred in using a separate transformer for each tube, transformers have been designed which have a plurality of secondary windings on one core.

In order that the current flowing through the secondary coil sections of such transformers may not exceed a maximum safe value, the transformers are provided-with magnetic by-passes including air-gaps of high reluctance through which the major portion of the energizing flux is shunted when current is flowing through the secondary coil sections. These by-passes have, in

Where the shunt pieces are integral parts of a core leg, their manufacture is expensive, because a special die must be used for each transformer having a different current output. Likewise, 'the manufacture of previously used shunt. parts which are separate from the main core, and of transformers in which such parts are incorporated, has been attended with difiiculties. This is due to the fact that such parts have been assembled in such a manner that the butt joint formed between the part and the main core was parallel to the flat surfaces of the air-gap. Thus, when heavy pressure was applied in order to secure a good butt joint, the length of the airgap was varied enough to make accurate control of the shunt path reluctance difficult, if not impossible. Moreover, a special die was necessary for each shunt part designed for a secondary of different current output. That was true because the part had to be varied in width or length in order to vary the reluctance of the air-gap.

It is a further object of my invention, therefore, to provide a multiple secondary circuit transformer whose magnetic shunt parts may be made inexpensively, without requiring a new die for each transformer of different current output and yet which shunt parts will provide magnetic by-passes of the proper reluctance for all transformers of nearly the same rating in which they are used. Moreover, it is my aim to provide a transformer in which the reluctances of the magnetic shunt paths can be accurately controlled.

Referring now to the practice of my invention and directing attention to Figure 1, it will be seen that my transformer consists of a core comprising two legs I and II interconnectedat their ends by members I2 and I3. Primary coil section P is mounted on the leg I0 and extends over substantially the entire length of that leg. Secondary coil sections S1, S2, S3 and S4 are mounted on the leg II. The core members are preferably formed of laminated magnetic steel and they are held together by core bands I4 and I5, which are preferably of magnetic material. The core also includes a T-shaped shunt member I6 abutting the leg II at about its midpoint and two- L- shaped members I! and I8 which abut the leg I I on opposite sides of its midpoint. The secondary coil sections are mounted on the leg II in such a manner that a separate magnetic shunt path is formedaround each coil section by the T-shaped member I6 and or one of the L-shaped members I1 and H3. The L-shaped member I! extends closely toward but does notv abut the leg I2, forming therewith an air-gap G1 of high magnetic reluctance. Similarly, air-gaps G2 and G3 are formed between the T-shaped member I6 and the L-shaped members I1 and I8 respectively. and air-gap G4 is formed between L-shaped member I8 and the leg I3. Where the secondary coil sections S1, S2, S3 and S; are of like current and voltage ratings; the air-gaps G1, G2. G3 and G4 have equal reluctances. This condition normally obtains where the loads of the coils are substantially equal. On the other hand, where the loads are unequal and the current and voltage demands on the secondary coils vary accordingly the air-gaps are adjusted so that the power delivered by each coil section will correspond to the need of its load. The manner of securing the members I5, I1, and I8 in place is not shown in Figure 1 but is similar to that which Will be described later in connection with Figures 3 and 4. Like the main core members, the shunt members are preferably made of laminated ma netic steel.

The primary coil P is energized through leads I9 and 20 from a suitable source of alternating current electrical energy H, such as a standard single-phase (SO-cycle source of supply at 110 volts. As the current in the coil P rises and falls between a maximum positive and 'amaximum negative value in conformity with the alterna tions of the electromotive force impressed across its terminals, an alternating magnetomotive force is induced in the transformer core. This magnetomotive force causes the rise and fall of a magnetic flux which traverses the core and links the coil sections of the secondary windings.

The coilsections comprising one secondary winding have their one terminals grounded, the grounded terminals preferably being those whose grounding places the coils in series, their other terminals being connected across the load of the winding. With this arrangement, the volt age across the load is approximately double that across the terminals of any one coil section and yet the voltage to ground at no point exceeds the maximum safe value approved by the fire underwriters. Thus the coils S1- and S2 have their one terminals grounded to the-core at 22 and 23 and their other terminals are connected across a negative load. such as the fluorescent luminous tube Tl illustrated, by the leads 24 and 25. Similarly the one terminals of the coils S3 and S4 are grounded to the core at 26 and 21 and their other terminals are connected across the terminals of the luminescent tube T2 by the leads 28 and 29. The core itself is preferably connected to ground, as at 30.

The transformer preferably is enclosed in a casing 3| having a cover 32. A suitable way of supporting the transformer in the casing is by resting it on the bases 33 and 34, the basesin turn resting on the bottom of the casing. The casing preferably is then filled with an insulating compound to prevent the destructive effects of moisture and ozone on the core and coils.

As the flux induced in the main core by the flow of current in primary coil P rises and falls in value, electromotive forces are induced in the secondary coils. When the potential across the terminals of the tube Ti is sufficient to ionize the gas therein, a current at once flows through the tube and its winding, which comprises coils S1 and S2. The current flowing through coils S1 and S2 sets up a magnetomotive force which opposes the coursing of themain flux. Accompanying this back magnetomotive force, a portion of the main flux is diverted around the coils S1 and S2 through a magnetic shunt path of high reluctance.' Assuming that the flux is coursing in the direction of the arrows, as seen in Figure 1, that is, in a clockwise direction, at the moment under discussion, this shunt path will be from the leg I0 through leg I2, air-gap G1, L-shaped member II, air-gap G2,.T-shaped member I6, leg II and leg I3, back to leg I II when the tube T2 is not operating. All the main flux will still link the coil sections S3 and S4 at this time. Similarly. when tube T2 becomes ionized, but tube T1 has not yet become ionized. the main portion of the main flux will be diverted through a shunt path through leg I0, leg I2, leg II, T-shaped member I6, air-gap G2, L-shaped member I8, air-ga G4. and leg I3, back to leg I0. Thus the main, flux will still be linking the coil sections Si and S2. When both tubes become ionized, the major portion of the main flux will be diverted through a shunt path comprising leg I0, leg I2. air-gap G1, L-shaped member I1, air-gap G2, T-shaped member I6, air-gap G3, L-shaped member I 8, airgap G 4-, leg 13 and back to leg l0. Although in the conditions of operation set forth-above the major portion of the main flux is by-passed around the secondary winding or windings, enough flux still links the coil sections of the operative winding or windings to maintains. steady flow of current through tubes Ti and T2.

It may happen that one secondary winding becomes grounded. Such a condition may be caused by the formation of a conductive film of moisture, atmospheric impurities, matted insect bodies, and the like between the terminals of the tube load or between terminals and a grounded part of the system. When such a condition exists, the operation of my transformer will be the same as that obtaining when the load is ionized and conductive while operating normally. Thus, if the tube Tris grounded, the current induced in its secondary coil sections S1 and S2 will generate a back m'agnetomotive force opposing the coursing of the main flux and causing it to seek a path of high reluctance through the magnetic shunt path, including leg l2, air-gap G1, member 11, gap Gamember l6 and leg ll. Excessive current will therefore not begenerated in the coil sections S1 and S2 and overheating of these coil sections, with consequent destruction of their insulation, will be prevented. The shunt construction provided for the coil sec tions S3 and S4 will likewise protect those coil sections from excessive current, and consequent overheating, if the winding which they form -becomes grounded.

Where one winding becomes open-circuited, as for example, by the breakage of the tube or tubes in its load, the other winding will continue to operate normally. Thus, if the tube T1 becomes broken, no current will flow in the coils S1 and S2 comprising its secondary winding. The main flux will continue to link those coils and also the coils S: and S1 until the tube T2 becomes ionized, as in normal operation. A similar condition will obtain if it is the tube T: which breaks, the

other tube T1 continuing to operate normally.

Where one of the coil sections becomes open-- half-cycle of the impressed electromotive force. The flux will then be coursing in a direction opposite to that indicated by the arrows, but the paths it follows will be identical for the same condition of operation.- Due to persistence of vision, the luminescent tubes, which are rendered ionized and luminous 1-20 times a second where a 60-cycle source of electromotive force is used, will, appear .to be continually lighted.

From an inspection of Figure 1, it will be apparent that it is a very simple matter to vary the lengths of the air-gaps. The legs'l2 and I3 and the members l6, l1 and I8 can be moved either to the right or to the left a suflicient amount to vary the reluctances of the air-gaps G1, Ga, Ga and G1 as desired. Because of this, it is not necessary that members I6, 11 and IB be made to different sizes for transformers of. different ratings. For this reason, different dies are not needed for manufacturing the shunt parts for difierent transformers and thus an item of expense in manufacture is eliminated.

It will further 'be observed that informing a tight butt joint between the members l6, I1 and I8 and the leg H, the reluctance of the air-gaps G1, Ga, Ga and G4 is not varied since the force exerted to move the shunt members firmly against leg I l is applied in a direction parallel to the surfaces of the air-gap faces. The force used for this purpose is ordinarily between ten of differences in securing the shunt members is an exceedingly important factor. It assures controlled operation of the transformer.

My transformer has also many advantages in operation. A shunt path is provided for each secondary'coil section, so that danger of 0veroperate in 'anormal manner as is more particularly described in the preceding paragraph.

Should one coil, say the/coil S1, become grounded, its winding will be rendered inoperative but no dangerous condition of excessive current flowing through it will exist, and the other winding will continue to operate in a normal manner. The voltage induced in the other 0011 S: will be insuflicient to ionize the gas in the tube T1, hence no current will flow in tube T1, 0 the coi B:- The current in the grounded coil 81 will not reach an excessive value because a counter-magnetomotive force will be generated by that coil as the heating any coil section is'avoided. Flexibility is thus achieved since any grouping of secondary coil sections is possible without danger of overheating. A high degree of eificiency'is achieved since the flux by-passed around each secondary coil when there is current fiowingthrough it nevertheless continues to link the as yet un-operated coil sections.

It will be understood that my transformer is capable of being modified in various ways. Thus,

where the load of each secondary winding as grounded at its mid-point, the coil sections may be connected in opposition, a complete circuit be ing formed between each half of the load and short-circuit current begins to flow in it. This back magnetomotive force diverts the main flux around the coil S1 through a shunt path of high reluctance from leg l0 through leg: l2, air-gap G1, L-shaped member l1, leg II, and member 13 back to leg 10. Similarly, individual magnetic shunt paths are provided for each of the other coil sections and prevent an excessive short-circuit current from flowing in them should they become grounded. In fact, in my transformer the short-circuit current is about the same as the normal load current.

It will be understood that the operation of my transformer under the various conditions ,enumerated above will be the same during the other the corresponding coil section. With such a connection, thegrounding or open-circuiting of one coil section or of the half of the load corresponding to one .0011 section will not render the other coil section and its half of the load inoperative. with the coils connected in opposition; however, the'maxlmum potential difference available for energizing a load is about seven thousand five hundred volts., Only tubes which are half or less than half the size of the largest tubes energizable by a series circuit can be used in such a circuit.

Also, as has been previously indicated, the coil sections may be connected in any grouping. Thus coil 81 may be grouped with coil S4 and coils S2 and S: may be united to form the two secondary windings. It is also possible to form one winding of the coils S1 and S: and the other of coils S2 and S4. A still further possibility is to have each coil constitute a complete and separate winding.

It is to be understood that my invention is not limited to a transformer having two secondary windings but may have only one or more than two windings, up to a reasonable number.

Where tube loads and coil sections of diiferent voltage ratings are employed, the corresponding air-gaps are adjusted tovary the reluctance of the shunt paths in accordance with the relative operating Voltages of the various secondary coils. Thus, if the tube T1 has a higher voltage rating than the tube T2, the series-connected coil sections S1 and S2 will have a greater number of turns than the coil sections S3 and S4 and will operate at correspondingly higher voltages. In order that sufiicient voltage may be induced ill coil sections S1 and S2 to maintain the tube Tl in an ionized condition after it has struck and current is flowing through the circuit. the airgaps G1 and G2 are adjusted so as to have a higher reluctance than the gaps G3 and G4. As has already been indicated. this is merely a matter of changing the relative positions of leg l2 and shunt members 11 and 56 to increase the lengths of air-gaps.

Considering now another embodiment of my invention, attention is directed to Figure 2 in which I have shown a shell-type transformer embodying my invention. The transformer comprises a core with primary and secondary windings mounted on the core. The core comprises outer legs and 36 and a centrally disposed core leg 3'8 parallel to the outer legs. ends of the log 35 and the ends of leg 31 are interposed short bars 38 and 39. Likewise, short bars 40 and 4| are positioned between the ends of leg 36 and the ends of leg 31. The parts are held in firmly abutting relationship by the core bands 43 and 42. The core preferably is grounded as at 44. Magnetic shunt paths of high reluctance are formed by the L-shaped members 4546, 41-48, 49--50, 5l-52, 53-54, and 55-56, which are so disposed as to abut the central core leg 31 at their one ends. Each L-shaped member extends around a secondary coil sectionand forms an air-gap with one of the short bars 38, 39, 46 and 4! or with the adjacent L-shaped member. The air-gaps so formed are indicated by the reference characters G1, G2, G3, G4, G5, G6, G7, G8, G9, G10, G11, and G12. as shown in the drawings.

The members 45 and 41 may be placed in backto-back relationship with a space A separating them, as shown, or if desired, they may be made in one T-shaped integral piece, or the member 45 may be turned around so that its tip will form an air-gap with member 41. Likewise, the members 46 and 48 may be in back-to-back relationship and separated by a space B, as illustrated, or they may be integral, or member 46 may be turned around. Illustratively, the magnetic shunt pieces. are secured to the central core leg 31 to insure silent operation in the manner shown in Figures 3 and 4. The shunt parts 55 and 56 illustrated are enclosed in a metal clamp 61. an insulating pad 68 being interposed between the clamp and the shunt parts. The clamp has two ears 69 and 10 drilled to receive a bolt 1 I. Washers 13 and 14 insulate the bolt head and the nut 12 from the cars 69 and 10. The nut 12 is turned until the clamp 61 holds the parts firmly together. It will be understood that any other suitable manner of securing the shunt parts to the core may be employed, the one shown being merely illustrative.

Between the 1'.

The primary winding consists of two elongated coil sections Pi and P2 connected in series by a lead 53 and mounted on the legs 35 and 36 respectively. These primary coils are energized from a source of alternating current electrical energy 56, such as a standard -volt 60-cycle source, through leads 59 and 66. The construction noted is compact and assures excellent transference of heat produced under operation conditions.

Three secondary windings are formed by the coil sections S1, S2. S3, S4, St. and Se, all of which are mounted on the central leg 3i. Coils S1 and S2 connected together in series form one winding energizing the tube T1 through leads 6i and 62. A second winding is formed by serially-connectedcoils S3 and S4 and energizes tube T2 through leads 63 and 64. The third winding comprises seriesconnected coils S5 and .Ss and energizes tube T3 through leads 65 and 66. The secondary coils are preferably grounded at their interconnections. Where the load of a Winding is grounded at its mid-point. however, the coils may be connected in opposition, a complete circuit then being formed including each half of the tube load and the corresponding secondary coil.

When the transformer is used indoors, it need not be enclosed in a casing. In outdoor use, however a casing is necessary. For the sake of clarity in the drawings, none. is shown in Figure 2, but a casing similar to the one shown in Figure i may be used where desired.

The operation 01 this transformer is similar to the operation of the transformer of Figure l which has already been described, with the ex- I ception that two main magnetic paths are provided and there are two magnetic shunt paths associated with each secondary coil section. Thus, assuming that the flux is coursing in the direction'of the arrows, it will consist of two parts going from the legs 35 and 36 respectively, through the bars 38 and 40 respectively, into the central leg 31, where the two parts unite and link the secondary coils. At the right hand end of the member 31 the flux separates into two parts again, traversing the bars 39 and 4|, respectively, and returning to the legs 35 and 36 respectively. In normal operation, as the tube Tl becomes ionized and conductive due to the rising of the electromotive force induced in its secondary winding coil sections S1 and S2 under excitation of the primary winding by the potential impressed across its terminals, a countermagnetomotive force is generated by the current flowing in the coils S1 and S2. This forces the major portion of the main magnetic flux to seek a path of less reluctance. .Two such paths are provided, from the leg 35 through bar 38, airgap G1, L-shaped member 45, leg 31, member 41, air-gap G3, member 49, member 31, and bar 39, back to leg 35, and from leg 36 through bar 40, air-gap G2, member 46, leg 31, member 46, air-gap G4, member 50, member 31, and bar 4| back to leg 36. The flux at this time continues to link the other coil sections S3, S4, S5, and Se, but passes around the coils S1 and S2 as outlined above, so that an excessive current does not flow in those coils. Similarly, the coil sections comprising the other windings will be by-passed when their loads are operating. Should all the loads be operative at the same time, the major portion of the main flux will pass through two paths of high reluctance excluding the member 31 and including all the L-shaped shunt members and their associated air-gaps.

As explained more fully in connection with Figure 1, safe'operation of the transformer will be assured under conditions of grounding or open-circuiting of a whole secondary winding or of one coil section of that winding.

As in the transformer shown in Figure l, the shunt parts in the embodiment of Figure 2 need not be of a different size for each transformer which varies slightly in current output. The reluctance of the shunt paths readily can be varied simply by moving the parts to the left or right as shown in Figure 2. Thus, a special die is not necessary to make shunt parts for different transformers, and the expense of their production is minimized. An accurate adjustment of the reluctance of each shunt path is possible because, in tightening the butt joint between the shunt part andthe main core member 31, any change of position ,of the shunt part will not vary the length and reluctance of the air-gap.

Instead, such movement of the shunt part will be in a direction parallel to the surfaces of the air-gap. A further advantage of this transformer is that it can be assembled with facility. It is a simple matter to mount the various secondary coil sections and shunt pieces in their proper positions on the central leg 31 as a first step andthen assemble the other parts about the leg 31.

Although I have illustrated a transformer having three secondary circuits, it is to be understood that any other number of circuits may be provided. Any number of secondary coil sections may be mounted on the core from one up to any reasonable number.

It will-be seen that there has been provided in my invention a system and apparatus for the illumination of luminous tubes or for the operation of other negative loads in which the various objects hereinbefore set forth, together with many practical advantages, are successfully achieved. The "apparatus includes simple parts which are inexpensively manufactured and which may be accurately assembled with a minimum of difficulty. The construction is compact. Extraneous magnetic flux leakage is low. Heat dissipation is high. Operation of the apparatus is" characterized by safety, flexibility-andeflil-- ciency.

As many possible embodiments may be made of my invention and as many changes may be made in the embodiments hereinbefore set forth. it will be understood that all matter described herein,- or shown in the drawings, is to be interpreted as illustrative and not in a limiting sense.

I claim:

In electrical transformer apparatus of the character described, in combination, a shell-type transformer core; a primary winding comprising two coil sections mounted one on each side of the outer legs of said core; one or more secondary windings mounted on the central leg of said core, each of said secondary windings comprising two coil sections having their one terminals grounded to place said coil sections in series; and L-shaped magnetic shunt parts abutting said central leg and spaced between adJacent coil sections and extending substantially but not completely around each of said coil sections, thereby forming magnetic shunt paths of high reluctance which exclude the coil section when it is operating under closed-circuit or shortcircuit conditions.

CHARLES PHILIPPE BOUCHER. 

